//tools/gazelle:gazelle runs the repository’s Gazelle language plugins.
Repository-wide directives remain in root BUILD.bazel, where Gazelle discovers
them for all packages. Root //:gazelle and //:gazelle_bin remain compatibility
entry points.
//tools/gazelle:gazelle_python_manifest.update refreshes root
gazelle_python.yaml; //tools/gazelle:gazelle_python_manifest.test validates
its integrity against root requirements.txt. Keeping the manifest at the
repository root preserves Python dependency discovery in every package.